Core stock paper is designed specifically for tube and core production, such as for tubes used in retail and commercial rolled towel and tissue products. As used herein, the terms “core” and “tube” are interchangeable. Core stock paper (i.e., the paper or paperboard from which the cores are made) is generally stiff, thick paper and may have a single-ply or multi-ply structure.
As used herein, the term “multi-ply” refers to paper having at least two plies, or layers. For example, the plies may be formed from separate layers of furnish in the papermaking process. As used herein, the term “furnish” refers to the material stock from which the paper plies are made. The furnish may include cellulose, such as cotton, linen, or alpha cellulose extracted from wood pulp, or any other furnish component known to those of ordinary skill in the art.
The furnish may also include size. As used herein, the term “size” refers to a substance that is incorporated into the paper (e.g., mixed in the furnish, added to the top layer of wet furnish during the papermaking process) to change the water absorption and/or wear characteristics of the paper made therefrom. For example, increased amounts of size may result in a reduction of the paper's tendency when dry to absorb liquid (i.e., an increase in the paper's hydrophobicity), and may also affect the finish and surface bond strength, and decrease the surface porosity, of paper made therewith.
Core stock paper is typically manufactured on a papermaking machine, such as a single fourdrinier wire or a single cylinder former, or on a series of formers. Multi-ply papers may be made on multi-cylinder former machines. Generally, these machines and processes limit the amount and/or application site of size incorporated into the paper. For example, fourdrinier machines only allow for the addition of size on the top layer of the paper during the wet process (e.g., after the furnish has been layered on the machine). Multicylinder machines traditionally add size to all of the plies.
Once formed, the paperboard may be wound on a corewinder to produce a tube or core onto which a tissue/towel web is would. To produce the tube, one or more strips of the paperboard is wound on a mandrel and glued. The amount of glue used and the location of glue application may vary based on the paperboard characteristics and the desired tube characteristics. For example, to form a 2-ply tube (i.e., 2 plies of paperboard), glue is typically added to the entire surface of the paperboard during core-forming. For a 1-ply tube, glue is usually added to the edge of the paperboard sheet (e.g., approximately the last quarter of the sheet). The tube may subsequently be cut to the desired length.
Generally, the physical properties of the paper, including basis weight, plybond (ZDT), smoothness, and tensile strength are important in forming a strong, rigid tube that meets the demands of high speed rewinders and also resists crushing from packaging, loading, and transportation/delivery. Also critically important is the glue absorption property of the paper, which dictates the amount of glue necessary, and the distribution of the glue, that may be applied on the core-forming machines during the process of making the tubes.
It would be desirable to provide core stock paper having improved properties.